Some recent internal combustion engines have a cylinder head provided with a divided port mechanism. Such a cylinder head has inlet ports divided into top and bottom portions by a divider plate that may also be called a “tumble plate.” By controlling an intake air flow control valve that is positioned at the inlet side edge of the inlet port, the intake air that is introduced from the inlet port to a cylinder bore is deflected thereby intensifying a tumble flow (vertical eddy flow) that is generated in the cylinder bore, so that the gas mileage, etc., is improved (See Japanese Laid Open Patent No. 2001-193469).